Pivoted discoid heart valve having a changing pivot axis

ABSTRACT

A HEART VALVE PROSTHESIS HAVING A DISCOID POPPET MOUNTED THEREIN FOR PIVOTAL MOVEMENT BETWEEN A CLOSED AND OPENED POSITION. THE POPPET IS SUPPORTED FOR MOVEMENT BY OPPOSED, SPACED SUPORTED STRUTS WICH FORM AN ECCENTRIC PIVOT POINT FOR   OPENING OF THE VALVE AND A CHANGING PIVOT POINT FOR CLOSING OF THE VALVE. THE SPACING BETWEEN THE STRUTS IS SUFFICIENT TO ENABLE ROTATIONAL MOVEMENT OF THE POPPET DURING OPERATION.

United States Patent 1111 3,824,629 Shiley [451 July 23, 1974 1 PIVOTED DISCOID HEART VALVE 3,416,159 12/1968 Smelloff et a1 ..3/1 HAVING A CHANGING PIVOT AXIS 3,448,465 6/1969 Pierce et a1 ..3/1 3 464 065 9/1969 Cromie ..3/ 1 761 t.D1dP.ShiIe,1102I-I a] 'z'g Ana. (ylam .5 3,476,143 11/1969 Kaster ..3/1 x [22 Filed; May 1971 FOREIGN PATENTS OR APPLICATIONS [21] Appl. No.: 140,900 15,264 0/1910 Great Britain ..137/527 558,773 1/1944 Great Britain ..137/527 Related pn u 0m 21,792 1/1917 Denmark ,.137/527.s

[63] Continuation of Ser. No. 809,754, March 24,

1969, abandone Primary Examiner-R1chard A. Gaudet Assistant Examiner--Rona1d L. Frinks 52 us. (:1 ..3/1, 3/DIG. 3, 137/5278 Y- Knobbe & Martens [51] Int. Cl. ..A6lf l/22 [58] Field of Search .3/1, DIG. 3; 137/527, 527.4, ABSTRACT 137/ 5278 A heart valve prosthesis having a discoid poppet 56 f mounted therein for pivotal movement between a I 1 Re cued closed and opened-position. The poppet is supported UNITED STATES PATENTS for movement by opposed, spaced support struts 'which form an eccentric pivot point for opening of the X valve and a changing pivot for closing of the 2,301,859 11/1942 Dauster ..137/527 va|ve The spacing between the struts is ffi i t to 3,365,728 1/1968 Edvvards Ct a]. ..3/1 enable rotational movement of the poppet d i 3,367,364 2/1968 Cruz et al. ..3/1 X operation 3,370,305 2/1968 Goott et a1 ..3/1 3,374,489 3/1968 Diaz ..3/1 23 Claims, 11 Drawing Figures.

PIVOTED DISCOID HEART VALVE HAVING A CHANGING PIVOT AXIS RELATED APPLICATIONS This application is a continuation of copending application Ser. No. 809,754, filed Mar. 24, I969 entitled PIVOTED DISCOID HEART VALVE HAVING A CHANGING PIVOT AXIS and now abandoned.

This invention is directed to a heart valve prosthesis for use in place of defective natural heart valves.

Heart valve prostheses, like the natural heart valves, are hemodynamically operated by the pumping action of the heart. Effective operation of such valves requires that the valve poppets be light in weight but yet'very durable and resistant to wear. The valve body must be constructed to evenly distribute forces uniformly across the surfaces of thepoppet. Additionally, the valve must open sufficiently wide so that the blood flow is not restricted and the valve function must not be destructive to the blood pumped therethrough.

Normally the prostheses include either a ball type valve poppet or a discoid poppet constructed from a filled silicone rubber whichis relatively resilient, soft and heavy, These valves are hemodynamically operated, for example, in the aortic valve, by the pumped blood forcing the poppet out of sealing relationship with the valve seat. The pressure and time required to open the valve is dependent on the size and weight of the poppet and any other resistance to opening offered by the valve structure.

Lateral forces and nonsymmetrical forces which operate to restrict axial excursion of the poppet must be reduced to aminimum to prevent large pressure gradients across the valve, wear of the valve poppet and thrombus buildup on the valve body.

Butterfly valves having an off-center, fixed hinge mounting the valve leaf or poppet for pivotal movement have been used to lower the pressure gradient across the valve. It has been found, however, that a protein buildup occurs inthe region of the fixed hinge with such valves. This buildup eventually limits movement of-the valve poppet causing ultimate loss of the valve function.

This invention is directed to a heart valve prosthesis which includes a ,discoid; valve poppet mounted for rotational andpivotal motion about camming surfaces attached to an annular valve ring or body. The hingelike movement is about a continually changing imaginary hinge point on the valve poppet rather than about a fixed hinge. The valve port is opened and closed by the pivotal movement of the valve poppet on the camming surfaces.

The camming surfaces are formed in one embodiment by a curved strut which extends into the valve port and supports the poppet for pivotal movement out of contact with the valve ring. The prosthesis also includes a suture cloth for attachingthe valve ring to the heart tissue.

One feature of the heart valve prosthesis of this invention is that the pressure required to open the valve balanced thereby reducing the shock of closing.

Another feature of the heart valve prosthesis of this invention is that thevalve life is extended since the operating forces are distributedon the surface of the valve poppet by rotational movement of the poppet during hemodynamic operation of the valve.

Yet another feature of the valve of this invention is thatthe poppet floats within limit defining members which enable pivotal motion of the poppet.

Another feature of the heart valve prosthesis of this invention is that a discoid valve poppet having a relatively thin portion of a lightweight, rigid synthetic resin is used.

Another feature of the heart valve prosthesis of this invention is there is no fixed relationship of the position of the poppet to the body: that is, the valve has all the advantages of a free floating poppet-valve plus the obvious advantages of a butterfly or rotating poppet valve.

Another feature of the heart valve prosthesis of this invention is that smooth rapid response of the valve to systolic contraction .or diastolic relaxation without lateral movement of the valve poppet can be consistently obtained.

is very low but yet the closing'forces on the valve are 7 Yet another feature of the prosthesis of this invention is that the support members supporting the valve poppet in the valve orifice are copiously washed by the blood passing through the valve.

These andother features of the heart valve prosthesis of this invention will become more readily apparent in view of the detailed discussion taken with the appended claims and the attached drawings wherein:

a FIG. I is a diagrammatic sectional view of a heart with the prostheses of this invention inserted in place of the natural mitral and aortic heart valves;

FIG. 2 is a top perspective view of the heart valve prosthesis constructed in accordance with this invention;

FIG. 3 is a top plan view of the prosthesis con structed in accordance with this invention;

FIG. 4 is a sectional view through the prosthesis of FIG. 3 taken substantially along lines 4-4;

FIG. 5 is a sectional view of the prosthesis of FIG. 3 taken substantially along lines 5-5;

FIG. 6 is sectional view of the prosthesis similar to FIG. 4 but showing the valve in an open position;

FIG. 7 is a diagrammatic view of one of the lower support struts and the valve poppet taken substantially along curved lines 7 -7 of FIG. 3 illustrating the manner in which the valve poppet moves during closmg; a

" FIG. 8 is a top plan view of an alternative embodiment of a heart valve prosthesisconstructed in accordance with this invention;

FIG. 9 is a sectional view of the heart valve prosthesis of FIG. 8 taken substantially along lines 9-9;

FIG. 10 is a top plan view of another alternative embodiment of a heart valve prosthesis constructed in accordance with this invention; and

FIG. I1 is a sectional viewof the heart valve prosthesis of FIG. 10 taken substantially along lines I I- l I.

Although the heart valve prosthesis of this invention is particularly adapted foruse as an aortic. valve, as shown diagrammatically in FIG. I, the heart valve prostheses 10and 10' may be made in various sizes for use as either an aortic, mitral of tricuspid valve replacement. The aortic valve prosthesis 10 is mounted in the aortic artery 12 at the natural valve ring 14 intermediate the aorta 12 and the left ventricle 16. The mitral valve prosthesis 10' is mounted in the left ventricle I6 on the muscle tissue 18 of the natural valve ring intermediate the left ventricle and the left atrium 20. For purpose of illustrating the prosthesis it will be discussed primarily as an aortic valve replacement.

As shown in FIG. 2, the structure ofthe prosthesis includes a metallic. valve ring or body 22 which defines a valve port and a seat for a valve poppet 24. A pair of opposing struts 26 and 28 each having a flattened U shaped configuration are attached to the valve ring 22 as by welding the ends of the strut elementsto the valve ring. An annular suture cloth 30 is held tightly within the outer periphery of the valve ring and has its free ends sewn together at 32 to form a means for connecting the valve to the heart or aortic tissue.

Referring now to FIGS. 2, 3 and 4, it is shown that the valve poppet '24 comprises adisc having an outer an nular portion 36 and a thinner central portion 37 (see FIG.;4). The thickerouter annular portion 36 is formed with a radial taper on both the upper surface 38 and the lower surface 40. The outer peripheral edge 42 of the disc" 24 is rounded so that it can seat in closing relationship with the inner surface of the valve ring 22. The valvepoppet is just slightly smaller in diameter than the valve ring 22 so that when it is in the closed position it is supported by the struts 26 and 28. The upper side ofthe disc 24 isprovided witha central circular'depression 44 peripherally defined by an annular vertical side wall 46. The side wall 46 is connected to the uppersurface '38 in a smooth curved shoulder 50 and to the Iowerwall 52 of the depression44 by ajuncture '54 having a relatively large radius vof curvature. The lowerside of the disc subjacent the depression 44 is a smooth, flat, circular surface 56. The thicker outer annular portion 36"of the disc is separated from the thinner inner portion 37 .by the wall 46 intermediate the curved shoulder 50 and the juncture'54.

' Referringiagain to FIGS. 2 and 3, the support strut 26 includes a pair of divergent strut elements 58, a circumferentially curved base 60 and a pair of shoulders 61 which curve toward the plane ofthe valve ring forming a smooth curve intermediate the strut elements 58 and the base 60. In the preferred embodiment the strut elements 58 diverge-at an angle of about 45. The strut 26 is formed from arigid cylindrical metallic rod having a diameter, as shown in FIG. 4, sufficiently large so that its outer surfacematches the radius of curvature of the juncture S4; The radius of curvature of the base 60 also is substantially the same as the radius of curvature of the sidewall 46 of-the depression 44 as shown'in FIG. 3. The base'60 is maintained at a distance less than the radius of the valve ring from the inner periphery of the valve ring by the strut elements 62 to define an eccentric pivot point for the valve during opening.

Thelower support strut, as shown in FIGS. 3, 4 and 5 includes a pair of divergent strut elements 62 which are connected to a base 64 by means of smooth, downwardly curved shoulders 66 which curve away from the plane ofthe valve ring as best shown in FIG. 5. The base 64 forms a smooth downwardly extending arc curving away from the upper strut 26 intermediate the pair of shoulders 66 at the ends of the strut elements 62. The strut elements 62 extend radially inwardly for a distance greater than the radius of the valve ring 22and are inclined slightly away-from the plane of the valve ring. The shoulders 66 and the strut elements 62 form a continuous smooth, curved, camming surface over which the flat circular surface 56 of the poppet 24 and the lower tapered surface 40 can ride when the poppet is being closed during diastolic relaxation of the left ventricle. The camming surfaces on the shoulders 66 are substantiallysubjacentthe upper strut base 60 for defining aloose, off-centerpivot for the poppet. As-the poppet closes the eccentricity of the pivot point contact between the strut 28 and the poppet 24 decreases since the poppet rolls up the strut elements 62.

In the preferred embodiment, the strut elements 62 diverge at an angle of about I30". Due to thecurvature of the base 64 (FIG. 5), the lower surfaces of the poppet are supported primarily by the cam ming surfaces of the shoulders 66 and the portions of the strut elements 62'adjacent the base. When the valve is in its full closed position, as shown in FIG. 4, the lower surface of the poppet 24 contacts the lower struts 28 substantially along a diameter of the valve, i.e., a straight line on the lower surface of the poppet 24 connecting the points of contact of the strut elements 62 withthe poppet 24 would pass through the center of the lower surface of the poppet. 1 a

The spacing between the upper shoulders 66 on the lower strut elements 62and the base 60 of the upper strut 26 is smaller than thethickness of-the thickest part of the annular portion 36 of the poppet 24 intermediate the annular tapered surfaces 38 and 40.so that the valve poppet 24 cannot slip out of the valve assembly. This spacing enables the valve poppet to pivot smoothly on the camming surfaces of the strutelements 62 and shoulders 66 of the strut 28 and on the base 60 of the upper strut 26. The spacing is sufficiently large, however, so that the poppet 24 is able to rotate about the axis of the valve during its operation. During this pivotal and rotational motion the flat surface 56 and the lower tapered surface 38 of the valve poppet move over the curved surface of the strut elements.62 and shoulders 66 to provide a smooth openingaction of the valve in'response to systolic contraction of the left ventricle when the valve is used as an aortic valve for example.

In the preferred embodiment, the spacing between the struts'26 and. 28 is sufficient to enable the valve poppet 24 to open up to an angle 11' (see FIG. 6) of about 7O. from the plane-of the valve ring. It has been found in simulatedpulse duplicator tests for which the pressure gradient as a function of opening angle has been recorded, that satisfactory operation can be had even if the valve is limited to an opening angle a of 50. Thepreferred opening angle a ranges from 50 to 80 At values higher than 800 the pressure gradient is not reduced by an appreciable amount while the response time is increased due to the longer distance the disc must travel. a

The valve assembly includes, as best shown in FIG. 4, an annular retainer ring 70 having a series of circumferentially spaced, radially extending thread receiving apertures 72. The suture cloth 30 and a suture pad 74 are maintained in position in a curved channel 76 on the outer side of the valve ring by means of the retainer ring 70 The channel 76 is a smooth curved continuous integral channel for receiving the retainer ring and for pressing the suture cloth 30 into position, The suture pad and suture cloth are mounted to the retainer ring 70 prior to assembly on the valve body 22 by threads 80 which are passed through the apertures 72. Since with the pivotal valve disc 24 of this invention there does not have to be a sealing relationship between the outer edge 42 of the disc and the inner edge of the ring 22,

the valve ring may have a substantially flat inner surface (see H08. 9 and 10).

The struts 26, and 28 are cast on or welded to the valve ring prior to mounting the retaining ring thereon and after, the poppet 24 has been positioned inter mediate the struts. d

The suture pad 74 is a relatively rigid thick piece of Teflon, Dacron or other such material which can be penetrated with a sewing needle but does not have axial flexibility. The purpose of the suture pad is to provide body for sewing the valve to the heart tissue. The suture cloth itself may be Teflon, Dacron or similar polymeric materials.

The valve body 22 and the struts 26 and 28 are all metallic such as the strong, resilient, corrosion resistant cobalt alloys Haynes 25 and Stellite. The retainer ring 70 may be metallic, or may be a plastic, such as Nylon or Teflon, which has sufficient resilience to expand over the outer edges of the valve ring 22. I

The method of assembling the valve body 22,,the retaining ring 70, the cloth suture pad 74 and the suture cloth 30 is similar to that described in detail in copending application Ser. No. 67 3,144, flled Oct. 5, I967 by Donald P; Shiley, now U. 8. Pat. No. 3,534,41 l. Briefly the prosthesis is assembled by radially expanding the preassembled suture pad 74, the suture cloth 30 and the retaining ring 70 and snapping them over the lower outer edge of the valve body 22 into the channel. 76. Since the inside diameter of the retaining ring 70 is approximately equal to the outside diameter of the channel 76 of the valve body 22, the retaining ring 70 is forced over the upper or lower surface of the curved channel 76 by working circumferentially around the outer edge of the channel and taking advantage of the springy character of the ring.

During operation of the aortic heart valve prosthesis of this invention, as best shown in'FlG. 6, the valve poppet 24 is hemodynamically opened by systolic contraction of the left ventricle which forces blood against the lower surfaces 40 and 56 of the valve disc. The poppet immediately moves away from the lower strut 28 and into contact with the eccentric camming surface on the base 60-of the strut-'26 and pivots about the base of the strut element 26 ha rapid, smooth, uninterrupted rolling motion. The precise fitting of the curved section of the base into the juncture 54 of the depression 44 on the valve poppet enhances this motion so that relatively little pressure is required to open the valve. Consequently, the pressure gradient across the prosthesis 10 is up to 50 percent less than with either the ball or regular .disc heart valves. For example the pressure drop across the heart valve prosthesis of this invention varies from 4 to 20 mm of mercury whereas ball heart valve prostheses of comparable orifice size have pressure drops of from 30 to 50 mm mercury. The depression additionally reduces the weight of the valve poppet 24 and the inertial resistance to opening andclosing of the valve. Additionally, dueto the light weight of the valve poppet 24 and the eccentricity of the base 60, the initial opening gradients are on the order of2 to 5 mm of mercury.

During diastolic closing of the valve. the pressure in the left ventricle drops to 0 mm of mercury and the pressure of the blood in the aorta acts downwardly on the upper surfaces of the poppet forcing it away from the upper strut 26 and into contact with the lower strut 28. The outer edge 42 of the poppet may also abut the valve ring 22 so that the poppet initially cannot slide through the valve port. The path of movement of the poppet 24 over the lower strut 28 is best shown in F It]. 7. initial contact of the poppet 24 and the lower strut 28 is substantially in vertical alignment with the base 60 of the upper strut 26 so that the pivot point is highly eccentric and the initial closing pressure is distributed over a large portion of the poppet above the central plane of the valve ring. As the poppet closes, however, the distance between the pivot contact point and the center line of the poppet (See phantom center line of FIG. 7) decreases since the poppet rolls up the shoulders 66 and the strut elements 62. immediately prior to closing the pivot point is at about the center line of the poppet so that the downward forces which act on one 'half of the upper surface of the, poppet to close it are balanced by the similar forces which act on the other half of the upper surface of the poppetand tend to open it. This condition is attributable to the migrating pivot point which moves along the camming surfaces I 66, and 62 during closing of the poppet. The poppet, of course, continues to close due to the momentum developed during closing. The shock and force with which the poppet strikes the lower. strut 28 is reduced significantly by this migration of the pivot point during closing. The upper strut 26 limits pivoting of the poppet beyond the closed position.

It has been observed that, as the heart valve poppet pivotally opens and closes, the poppet momentarily floats between the upper strut 26 and the lower strut 28 and rotates in the plane of the valve body about the axis of the valve thereby evenly distributing the forces onthe valve poppet'and reducing problems of thrombosis and protein build-up concomitant to fixed hinge valve. For example, as viewed in FIG. 3, the valve poppet 24 rotates either clockwise or counterclockwise (depending on the force distribution) about the central axis of the valve during operation so that the contact between the valve poppet 24 and the base of the upper strut and the curved strut element surfaces and shoulder of the lower strut 28 do not always occur at thessame points on the poppet. The poppet of a valve constructed in accordance with this invention after several years a'ccelerated life test was found to have a negligible amount of evenly distributed wear. The projected life of the valve poppet based on these tests was over 20 prosthesis of this invention is shown in FIGS; 8nd 9. j

in this embodiment the U-shaped struts 26 and 28 are replaced by finger-like upper and lower struts 1'26, 127 and 128. As shown in FIG. 9, the strut 126 has a downwardly curved shoulder 130 with an end projection 132 which is a smooth curve of substantially the same-radius of curvature as the juncture 154 of the base and side wall 146 of the depression 144 in the I valve poppet. The lower struts 127 and 128 are prw vided with downwardly curved camming surfaces 134 and a rounded end portion 135 for permitting the valve to cam over these surfaces during closing.

The lower struts extend radially for a greater distance than the upper strut so that the ends of the struts are substantially coplanar and define an offcenter, initiaL'closing pivot point forthe poppet. The spacing vbetween'the ends 135 of the'lower struts 127 and 128 and the end 132 of the upper strut 126 is smaller than the thickness'of the outer periphery of the valve poppet so that the valve cannot slip out of the assembly. The spacing is sufficiently great, however, to pennit rotational movement of the poppet. The poppet disc is floatingly contained intermediate the upper and lower struts.

The operation of this valve is identical to that of the valve discussed with respect of FIGS. 1-7. During opening the poppet pivots in a smooth motion about the curved portion 132 of the upper strut 126. The poppet cams over the lower struts during closing with the points of contact moving toward the center line of the valve poppet to reduce the closing forces. The motion in opening and closing the valve is continuous and relatively effortless.

Again it has been observed with a valve constructed in accordance with FIGS. 8 and 9 that the poppet itself rot-ates during operation as well as pivotally opening and closing. This structure reduces the ,total valve weight by reducing the size of thesupport struts.

. Theembodiment of the heart valve prosthesis shown in FIGS. land 11 includes a conical valve poppet disc 224 which is floatingly mounted between spaced, substantially coplanar, opposing support struts 226 and 228. The valve disc 224 includes an annular outer peripheral upwardly inclined portion having an' upper surface 238 and lower surface 240 which are connected in a smooth curved edge 242 at the outer periphery of the disc. An annular groove 244 is formed in the truncated upper base portion of the upper surface'238. The upper support member 226 extends at an oblique angle away from the plane of the valve ring-222 and has an end portion 230 which depends downwardly therefrom. A shoulder 232 connects the main strut element 226 to the end portion 230. The end surface 234 of the support strut 226 has a radius of curvature substantially equalto that of the annular groove 244 in the upper surface of the disc.

The lower support strut 228 includes a pair of strut elements 262'which extend inwardly from the valve ring 222 and slightly away from the plane of the valve ring at their ends as best shown in FIG. 11. The base 264 of the lower strut is maintained substantially coplanar with the end 234 of the support strut 226 on opposite sides of the valve disc 224 (see FIG. II).

The valve ring 222 of this embodiment, as best shown in FIG. ll. includes an inner surface 266 which has such a large radius of curvature that it is substantially flat to permit laminar flow of blood through the valve port defined by the ring 222. The outer surface of the valve ring includes a pair of upper and lower outwardly extending annular flanges 268 and 270 which defined an annular channel having a flat lower surface 272. A suture cloth 274, a suture pad 276 and a retainer'278 are force fit into the channel so that the upper and lower edges of the suture cloth and suture pad extend slightly beyond the flanges 268 and 270 of the valve ring 222. Thus the suture cloth 274 can receive sewing thread and needle on either side of the flanges 268 and 270 to mount the valve prosthesis in the body. a

The suture cloth 274, the suture pad 276, and the retainer 278 are preassembled, as discussed with respect to the embodiment shown in FIGS. 1-9, by passing a thread 280 through the suture cloth, the suture pad, an aperture 282 in the retainer for sewing the ends of the suture cloth together and enclosing the retainer and the suture pad. A valve ring and retainer suture cloth assembly such as shown in FIG. 11 can be used with any of the embodiments of the valve prosthe sis of this invention since the valve ring is not required to provide a seating surface for the valve discsuch as disc 224 when the disc is in its closed position. The upper support strut 226 and the lower support strut 228 define the limits of the open and closed position of the valve poppet and only support the valve poppet when it is in these positions or when it is opening against the upper strut 226 or closing against the lower strut 228.

During operation of the heart valve prosthesis shown in FIGS. 10 and 11, systolic contraction of the left ventricle flips or pivots the valve poppet 224-upwardly, when'it is mounted in the aortic position, in a smooth continuous motion against the camming surface. 234-on the end of the support strut 226. The surface 234 has substantially the same radius of diameter as the groove 244 so that the pivotal movement of the valve poppet is continuous and smooth. In the full open position the disc is primarily supported by the end surface 2340f the strut 226. During closing upon diastole, the poppet outer edge 242 contacts the inner surface 266 of the valve ring 222 and the lower surface 240 of the poppet rolls along the camming surfaces of the strut elements 262 moving the pivot point inwardly toward a center line of the poppet thereby reducing theclosing force as the valve gets closer to the closed position. #In the closed position, the outer edge 242 of the valve-disc 224 does not contact the inner surface 266 of the valve ring but the spacing between these surfaces is so small that regurgitation through the valve orifice is insignificant.

The spacing between the support struts 228 and 226 is sufficient to permit rotational movement of the valve poppet during hemodynamic function of the valve at normal blood pressures and cycle speeds. This floating maintenance of the valve poppet intennediate the sup port struts again prevents protein buildup and throm bus formation at the support strut surfaces. I

Due to the configuration of the valve ring which can be used with the pivotal valve poppets of this invention, the outer edges of the valve poppets do not have to be sufficiently strong to support the poppet in seating relatially reduced. For example the maximum number of open and closing cycles per minute obtainable with the ball type aortic valve is about 800 whereas aortic flip valves constructed in accordance with, this invention have been operated at upto 3,500 cycles per minute, when opened to an angle of 70?.

Although the disc 224 been shown to be solid in construction, the lower surface of the disc can taper upwardly substantially parallel to the upper surface to form a substantially shell-like disc having ahigh pivot point. Furthermore, although the disc need not fit on the valve ring 222, the high pivot point disc can be constructed so that it does seat on the valve ring and swing away from it during opening action. The advantage of this type valve is that the valve structure can be very small while the response time and pressure drop across the valve are still maintained within acceptable levels.

lclaimz' l. A heart valve prosthesis comprising:

means defining a valve ring having a port therein;

means defining a movable valve said valve port; v valve poppet support members for enabling pivotal movement of said valve poppet relative to said valve'port between a closedposition and'an'ope position, said members comprising: I m

a first member on one side of said valve poppet contacting said poppet during opening; I a second member on the opposite side of said valve poppet contacting said poppet during closing; a camming surface on said second member cooperating with asurface on said valve poppet to define a moving pivotal axis during closing, said. camming surface being spaced from said first member by a distancesufiicient to enable movement of said pivotal axis from an eccentric position toward a diameter of said valve poppet therebyreducing the closing force of said valve poppet as said poppet moves toward the closed position, said distance being sufficient to maintain said valve poppet between said support members; and a means connected to said valve ring for attaching said prosthesis in place of a natural heart valve.

2. A heart valve as defined in claim 1 wherein said valve poppet has camming surfaces on each side thereof for cooperating with said first and second members for providingsmooth opening and closing of said poppet while reducing the closing force of said poppet.

3. A prosthesis as defined in claim 1 wherein said members for permitting pivotal movement of said poppet comprise a pair of spaced substantially U-shaped opposing members, each having a pair of strut elements and a base, said opposing members mounted on said valve ring on opposite sides of said poppet, one of said members defining a pivotal axis for-opening of said poppet and the other of said members defining said changing pivotal axis for closing of said poppet.

4. A prosthesis as defined in claim 3 wherein said opposing members extend radially inwardly from opposite sides of the inner surfaces of said valve ring so that their bases are substantially aligned in spaced relationship with one another.

5.- A prosthesis as defined in claim 4 wherein said poppet for closing valve poppet is a discoid having a first portion of a first. I thickness and asecond portion of a secondthickness 10 greater than said first thickness and wherein the spacing between the ends of said opposing members is greater than said first thickness but less than said second thickness.

6. A prosthesis as defined in claim 5 wherein said second portion is an outer annular portion of said valve P pp 7. A prosthesis as defined in claim 4 wherein the spacing between said opposing members is sufficiently large to permit rotational movement of said poppet.

8. A heart valve prosthesis as defined in claim 1 wherein said first and second members comprise a pair of U-shaped support struts, each having a pair of strut elements and a base, said strut elements diverging from said base attached to the inner surfaces of said valve ring and extending radially inwardly from said valve ring so that the bases of said U-shaped struts form a loose off-center pivot for said valve poppet.

9. A heart valve prosthesis as defined in claim 8 wherein the strut elements of one of said support struts is curved away from the plane of saidvalve ring to provide smooth camming surfaces for rolling pivotal movement of said valve poppet. I

10. A heart valve prosthesis as defined in claim 8 wherein said valve poppet has an annular curved sur face thereon having substantially the same radius of curvature as the base of one of said struts and-wherein saidibase is circumferentially'curved to engage said an nular curved surface. a

11. A heart valve prosthesis as defined in claim 1 wherein said first and second members are arranged so that the angle between said poppet in the open position and the plane of said valve ring is from about 50 to about 12 A heart valve, prosthesis as defined in claim 1 wherein said valve poppet support members comprise a first strut extending inwardly from said valve ring and having a depending curved end portion thereon and a pair of second struts extending inwardly from said valve ring in opposing relationship to said first strut, said first and second struts being on opposite sides of said valve P PP 13. A heart valve prosthesis as defined in claim l2 wherein said poppet has camming surfaces on one side thereof and said second struts include camming surfaces for cooperation with the camming surfaces of said poppet for smooth pivotal opening of said valve.

14. A prosthesis as defined in claim 1 wherein said valve ring has a substantially fiat inner surface which is of a slightly greater inner diameter than the outer diameter of said valve poppet.

15. A heart valve prosthesis comprising:

a valve ring defining a through valve port;

means defining a substantially discoid valve poppet;

a first strut member extending inwardly from said valve ring by a distance less than the radius of said valve ring and having a surface thereon for cooperating with one side of said valve poppet;

at least one second strut member extending inwardly from said valve ring and having camming surfaces thereon for cooperating with the other side of said valve poppet, said strut members being mounted on said valve ring and spaced from each other so as to enable rotational ,and pivotal movement of said poppet between an open and a closed position and i l to maintain said popmt in said prosthesis, said camming surfaces on said second strut member defining an eccentric pivotal axis for said valve poppet which changes to a less eccentric pivotal axis during movement of said valve poppet from the open to the closed position thereby reducing the closing force on said valve poppet as it nears its closed position, and

means connected to said valve ring for attaching said valvein'the place of a natural heart valve.

16. A heart valve prosthesis as defined in claim wherein said strut membersare substantially U-shaped metallic rods fixedly mounted on said valve ring.

17. A heart valve prosthesis as defined in claim 16 wherein said strut members comprise a pair of strut elements and a base and wherein said bases are substantially coplanar at an off-center position in said valve port.

18. A heart valve prosthesis as defined in claim 15 wherein said first and secondstrut members are aligned to support said poppet in closed position and to provide a predetermined stop for limiting the opening angle of said poppet and said strut members are spaced to permit said poppet to be free floating in said valve ring.

19. A heart valve prosthesis comprising:

means defining a valve ring having a valve port therein;

means defining a movable valve poppet;

means connected tosaid valve ring for defining a first changing pivotal axis for said poppet during opening of said poppet; means connected to said valve ring spaced from said I first axis defining means and defining a second pivotal axis which moves closer to the centerline of said poppet during closing of said poppet; and means for attaching said prosthesis to body tissue in place of a natural heart valve. 20. in a heart valve prosthesis having a valve ring with a valve port therein, a movable valve disc for substantially closing the valve port, support members connected to said valve ringmaintaining said valve disc in said valve and spaced on opposite sides of said valve disc forpermitting free floating of said disc between said support members and rotational and pivotal movement of said disc b'etween a port opening and a port cloaing position andmeans connected to the valve ring for aching the prosthesis in the place of a natural heart valve, the improvement comprising:

means for defining a changing pivotal axis during closing of the valve which reduces the eccentricity of the pivotal axis as the valve approaches, its closed ition thereby reducing the closing force of the valve disc. I 21. A heart valve prosthesis as defined in claim 20 wherein said means for defining a changing pivotal axis comprises a camming surface on the support members which cooperates with a surface on the valve disc.

22. A heart valve prosthesis comprising: a valve ring having a valve port therein; a valve disc having a top side and a bottom side and a concentric circular depression in the top side; and means floatingly containing the disc in the valve port during opening and closing comprising lower strut structure for supporting the bottom side of the disc on two s seed a surfaces durin closi a d a single up per stru t or engaging the op siti e of the 

